The present invention is directed to electric discharge and neutralization. More particularly, the invention provides a system and method for removing charges with improved efficiency. Merely by way of example, the invention has been applied to a semiconductor substrate and its associated structure. But it would be recognized that the invention has a much broader range of applicability.
A semiconductor substrate is often used for making an integrated circuit. The fabrication process uses various types of techniques, such as etching, deposition, and photolithography. During the fabrication, the semiconductor substrate and its associated structure are often transported from one location to another location. The transportation and fabrication processes may result in static charges located inside the semiconductor substrate and its associated structure.
These static charges can adversely affect subsequent fabrication or inspection processes. To reduce the adverse effect, a conventional pre-charging technique has been developed for SEM inspection. The pre-charging technique uses a flood gun to create strong and equalized charging on a semiconductor substrate and its associated structure. The charging can reduce or eliminate the non-uniform distribution of electrostatic charges generated prior to or and/or during the SEM inspection. But the pre-charging technique may result in image distortions in gray scale, reduced image sensitivity and resolution, and time-dependent location-related differences due to non-uniform charge leakage.
Additionally, to reduce the adverse effect on fabrication or inspection processes, some conventional techniques have been developed to remove electric charges. These conventional techniques include ionizer radiation and ultraviolet (UV) illumination. The ionizer radiation generates and transports the ionized air to neutralize electrostatic charges on the surface of a semiconductor substrate and its associated structure. This technique has been applied to wafer lithography, wafer transport, scanning electron microscopy (SEM) inspection, and atomic force microscopy (AFM) inspection. But the ionizer radiation technique often cannot effectively neutralize electric charges located inside an insulation film away from the film surface. Another conventional technique uses UV illumination. The radiated semiconductor substrate often includes grounded conductive traces. But the UV illumination technique usually cannot effectively neutralize electric charges far away from conductive traces.
Hence it is highly desirable to improve techniques for removing and neutralizing electric charges.